MASTER`S GUIDE TO: ENCLOSED SPACE ENTRY

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MASTER`S GUIDE TO: ENCLOSED SPACE ENTRY PAGE : 36 of 60 DATE : 01.07.14 PREPARED: MAR EDITION : 1.0 Oxygen in the atmosphere The oxygen meter should indicate around 20.8% oxygen in the space being tested. Always make sure your oxygen meter is properly calibrated. Never trust your own senses to determine whether the air in an enclosed space is safe. Many toxic gases and vapours can be neither seen nor smelled, nor can the level of oxygen be determined. It is important to understand that some gases and vapours are heavier than air and will settle to the bottom of an enclosed space. Some gases are lighter than air and will be found around the top of the enclosed space. Therefore, it is necessary to check all areas (top, middle and bottom) of an enclosed space with properly calibrated testing instruments to determine which gases are present. Atmospheres may be different in individual bays of the same tank. MARISCON GROUP 01.07.2014
MASTER`S GUIDE TO: ENCLOSED SPACE ENTRY PAGE : 37 of 60 DATE : 01.07.14 PREPARED: MAR EDITION : 1.0 If testing reveals oxygen deficiency, or the presence of toxic gases or vapours, the space must be ventilated and retested before entry. If in doubt, do not enter and consider seeking shore-side advice. Testing instruments When a Draeger tube or equivalent is used for detecting toxic gases, the sampling gas should have sufficient time to pass through the sampling hose. As a rule, if a manual hand rubber pump is used, approximately four squeezes are needed for each metre of the sampling hose. If battery driven pumps are used, approximately 10 seconds for each metre of sampling hose should be sufficient. Refer to manufacturer’s instructions. Atmosphere testing shall be performed: • before every entry when the space is vacant • after ventilation period • at least hourly • more frequently if conditions or suspicions warrant Guidelines for the use of personal gas detectors In spaces of complicated geometry with a high possibility of pockets of atmosphere with low O2 content, and where rescue operations may be difficult, such as tanks and voids, the use of a portable oxygen meter with audible alarm is strongly recommended. A multi-gas meter, capable of simultaneous monitoring of oxygen, combustible gases, hydrogen sulphide and carbon monoxide, should preferably be used. Note that carbon monoxide (CO) sensors may also be sensitive to low concentrations of hydrogen (H2). Therefore it is important to evaluate whether there is CO/hydrogen in the space. Anodes may generate hydrogen when in use. The personal instrument should be turned on before tank entry. If those entering are not wearing personal monitors, the person in attendance at the entrance should conduct regular tests of the atmosphere in the space. Calibration of monitoring equipment Ships should be equipped only with monitors that can be calibrated. Some types of monitors come with manufacturer-approved calibration devices – others should be sent ashore for calibration. Calibration on board must be carried out only by a competent officer. Monitoring equipment should always be marked with the due date of the next calibration. The equipment should not be used if calibration of the device is overdue. MARISCON GROUP 01.07.2014
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MASTER`S GUIDE TO: ENCLOSED SPACE ENTRY

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